Input: wacom - register an ac power supply for wireless devices

This is used by HID Bluetooth devices but also add some more information
to the USB Wireless Receiver.
We are just porting the bits from hid-wacom.c to the common driver here.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Przemo Firszt <przemo@firszt.eu>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
diff --git a/drivers/hid/wacom.h b/drivers/hid/wacom.h
index 98cb93f..0b89ee7 100644
--- a/drivers/hid/wacom.h
+++ b/drivers/hid/wacom.h
@@ -120,6 +120,7 @@
 	} led;
 	bool led_initialized;
 	struct power_supply battery;
+	struct power_supply ac;
 };
 
 static inline void wacom_schedule_work(struct wacom_wac *wacom_wac)